There are many known devices which include openings. Often the openings are necessary only for certain operations of the device. In other instances, the openings are unnecessary, and thus for optimal operation of the device. These openings must be plugged to prevent the internal components or areas from being exposed to the elements. Such openings therefore require plugs that can be removeably placed within the opening in order to adequately plug the opening. One problem associated with such devices occurs where there are numerous devices and the openings of those devices are not uniform in dimension. In such cases, it is costly to maintain an inventory of numerous plugs of various dimensions in order to plug all of the openings and to determine for each particular opening which size plug is needed.
One example of a device which includes such an opening is a manhole cover. Manhole covers are generally circular in shape and are adapted to cover manholes. Manholes permit workers to enter the sewage system to perform any necessary repairs and maintenance. Because manholes are generally formed from steel, they can be quite heavy and thus be difficult to remove from the manhole. Further, manhole covers usually do not include handles, which would facilitate in their removal, because most manhole covers must be flat, as they are often located in streets or on sidewalks. Thus, in order to remove the manhole cover from the manhole, tools have been developed which permit the user to more easily lift the manhole cover from the manhole. These tools, however, require that a small opening be made in the manhole cover.
While the openings in the manhole covers are necessary to permit the user to lift the manhole cover from the manhole, the opening causes the drawback that, during periods of rain, water is permitted to enter into the sewage system through these openings. Because many sewage systems are not designed to handle large flows of water, any additional water entering into the sewage system may cause severe problems in the sewage systems. During periods of rain, the amount of water flowing through the system increases, and if the rain is heavy enough, the excess water flowing through the system may cause overflows in the system, thereby causing untreated sewage to flow from the sewage system and into natural waterways, such as lakes, rivers, and oceans. Thus, it is important, in order to prevent the overflow of raw, untreated sewage, and thereby protect the public health, that, during periods of rain, the amount of water flowing through the sewage systems be limited as much as possible.
Although the water flowing through the opening of one manhole during a period of rain may be insignificant when compared to the total amount of water flowing through the sewage system, when the total number of manholes in the entire sewage system is considered, the amount of water added to the system during periods of rain can be substantial. For instance, in the county sewer system of Los Angeles, there are 140,000 manhole covers which amounts to approximately 1,500 square feet of openings. The water flowing through these openings during periods of rain is not insubstantial. This amount of water may be enough to overflow the sewage system or at least further exacerbate the problem. Thus, it is vitally important that the openings in the manhole covers be plugged when not being used to remove the manhole covers, so that water does not enter the sewage system through these openings during periods of rain.
Covering all of the openings in the manhole covers can be very difficult, however. In any one area, the manhole covers in use may have openings of different sizes. This would require that plugs of different sizes and shapes be carried by the user, and the proper plug be found for each particular manhole cover. This would increase the amount of time it would take to plug the openings, thereby increasing the labor cost for plugging the openings. It would also increase the inventory of plugs that would have to be maintained, thereby increasing the cost of inventory.
One proposed solution to the problem of using a single plug that can plug openings of differing sizes in manhole covers is a screw with a deformable rubber portion that is compressed and widened to fill the opening. The device has a base and a top portion that are attached to each end of the screw. The plug is placed into the opening and the base is tightened by screwing it onto the shaft of the screw, thereby decreasing the distance between the top of the screw and the base. The rubber portion, which is located between the top and base portion, is compressed when the base portion is screwed further onto the shaft of the screw. As the rubber portion compresses, it expands outwardly to fill the opening, until it reaches the side walls of the opening. The base is tightened until the rubber portion is firmly pressed against the walls of the opening, thereby plugging the opening. Because the rubber portion must be compressed to fill the opening, this plug may be used to plug any opening having a diameter that is between the diameter of the rubber portion in its relaxed state and in its compressed state.
This plug having a deformable rubber portion, although adequate for its intended use, has many drawbacks. For example, such plugs are hard to use and require a considerable amount of time to be properly placed within the opening and to be removed from the opening. Further, these plugs are subject to degradation due to the elements, because the rubber may degrade and the base, top, and screw portions may rust. Moreover, such plugs are difficult and expensive to manufacture.
Accordingly, it will be appreciated from the foregoing that there is a definite need for a self adjusting plug. The plug should be capable of easily and quickly plugging an opening with a substantially water tight plug. The plug should be adapted to fit in a variety of differently sized openings. It should also be easily removed from the opening and replaced into the same or another opening. It should not be subject to degradation by the elements and it should be lightweight and inexpensive to manufacture. The present invention meets these needs.